In surgery it is generally known to use a bone-patellar tendon-bone graft, taken from the knee of the patient, to replace the severely damaged anterior cruciate ligament (ACL). In a surgical procedure one bone graft is fixed into a drillhole made from the knee joint into the distal femur and another bone graft is fixed into a drillhole made into the proximal tibia. The bone plugs are fixed into drill holes with bone fixation screws and in most cases with so-called interference screws. A screw is installed into the space between the drillhole and the bone graft to lock the bone graft into the drillhole. The patellar tendon part between the bone blocks acts as a new ACL. The surgical technique of bone-tendon-bone procedure is described, e.g., in Bach, B. R., Potential Pitfalls of Kurosaka Screw Interference Fixation for ACL Surgery, American Journal of Knee Surgery, Vol. 2, No. 2 (1989) at 76-82 (Ref. 1), the disclosure of which is incorporated herein by way of this reference.
The fixation screws, like interference screws, are normally made of metal, like stainless steel or titanium, or of a bioabsorbable polymer, like polylactide. Metallic and/or bioabsorbable polymeric materials and composites, suitable for manufacturing of bone-tendon-bone graft fixation screws, are described in the literature. See, e.g., Barber, A. F., Burton, E. F., McGuire, D. A. and Paulos, L. E., Preliminary Results of an Absorbable Interference Screw, The Journal of Arthroscopic and Related Surgery, Vol. 11, No. 5 (1995) at 537-548 (Ref. 2); and Bach, B. R., Arthroscopy-Assisted Patellar Tendon Substitution for Anterior Cruciate Ligament Insufficiency, American Journal of Knee Surgery, Vol. 2, No. 1 (1989) at 3-20 (Ref. 3), the disclosures of which are incorporated herein by way of this reference.
The use of screws as fixation implants for bone grafts in bone-tendon-bone procedures is complicated by various facts:
the threads of the screw can cut the bone block to pieces during screw installation if the screw is too big in relation to the bone block and/or if the space between the drillhole and bone block is too small; PA1 the threads of the screw can damage the tendon during screw installation; PA1 the bone block (and the tendon) can rotate with the screw during screw installation so that the optimal position of the bone graft is lost and/or the bone graft is damaged; PA1 divergence of the graft and/or screw can occur; and PA1 the bioabsorbable screw can break during its insertion.
Such complications like those recited above are discussed in the above three references cited herein.